Re: [time-nuts] GPS DO Alternatives
Hi Unless the OCXO and PPS both stay within +/-50 ns (100 ns p-p) over the entire lock in period, the PLL will not lock up. If you slip outside that range the error signal changes sign. It drives away from lock rather than towards lock. The XOR and mixer phase detectors have this same problem. If you are averaging 100 samples and locking in 10 averages (unlikely), that comes out to < (50x10^-9/1000 = 5.0 x10^-11). That's not going to happen with an OCXO. It's unlikely to happen with an Rb. Lock up would occur in 1,000 seconds in this case. Can you divide the 10 MHz to widen things out - yes. If your OCXO is at 0.1 ppm, you would first look at dividing by 10,000. That would give you a range of +/- 500 us. At this point the same averaging and lock would occur in 10,000,000 seconds. Other than possibly not wanting to wait that long, the lock still is unlikely to occur. The time drift scales at the same time the lock time goes up. You still need a 5x10^-11 Rb to get it to lock up. The scale does not help for oscillator accuracy. It does help for GPS jitter, but that never factored into the analysis above. It was assumed to be zero. Starting out simple / easy and then boosting things up later sounds like a good idea. Some architectures simply do not lend themselves to a boost. --- One might also ask, if this is the problem, how is it solved? 1) Measure the PPS to GPS with a counter of some sort 2) Slip the PPS on the OCXO to get it near the "right" place 3) Monitor the offset with the counter to get a coarse lock 4) Possibly go through a few steps 5) Fire up the PLL In the case above you would need to get to ~ 1x10^-11 before you went into state 5. That's likely more than a few steps in part 4. Bob On Dec 9, 2012, at 6:26 PM, Hal Murray wrote: > > albertson.ch...@gmail.com said: >>> I don't think that is going to do what you want. The problem is what >>> happens if set and reset are on at the same time? > >> This would be the best case. The result will be random and we'd read an >> average value of 0.5 from the flip flop. > > The problem is that FFs don't work that way. > > There are two types of FFs. > > SR-FFs have set and reset inputs. Set turns it on. Reset turns it off. > These are level sensitive, not edge sensitive. If both set and reset are > active at the same time (overlap) you have to look in the data sheet to see > what happens. After the overlap, the last one active wins. > > Edge triggered D-FFs have data (D) and clock inputs. If D is high when clock > goes high, the output will be high. If D is low when clock goes high, the > output will be low. > > There are rules for FFs: Setup, hold, min high/low on the clock, ... Read > the data sheet for the whole list. > > >> I think you want everything to be edge triggered. The flip flop should look >> only at the leading edge of each pulse. > > That would be handy, but I don't know of any FFs that work that way. All of > the clocked FFs only have one clock. > > You might make it work by using the PPS as the clock with the D input hard > wired to 1. That will set the FF unless the reset is active. > > > albertson.ch...@gmail.com said: >> You don't get a PPS from the OXCO. It runs at 10MHz (Or whatever you like) >> so it resets the flip flop every 100 nanoseconds. > >> The way this works is the PPS from the GPS sets the FF to "1" once per >> second and then some time later the OXCO resets it back to zero. If we >> sample the FF at some fixed time after the PPS and that fixed time is less >> then the OXCO period then the FF will be either 1 or 0. THe computer tries >> to drive the OXCO so that the sampled value is 0.5 on average. So it looks >> at the last 1000 samples and tries to hit "500". > > How are you going to implement that fixed time delay and sampling? I don't > see a simple way to do it. > > What is the correct delay? How about 0? > > In general, when people start adding things like "fixed delays", I start > thinking "kludge - there must be a better way". > > > > There is another problem with using the OCXO output (100 ns) directly. How > do you eliminate aliasing/beats? Suppose the OCXO is running at exactly 9 > MHz. If you average over 1000 samples, you'll get your 0.500 . If you look > carefully, you can find a pattern. > > There is probably some simple math in here, but I'm not enough of a PLL > wizard to be able to describe it. Capture range and things like that. > > > > -- > These are my opinions. I hate spam. > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instru
Re: [time-nuts] GPS DO Alternatives
albertson.ch...@gmail.com said: >> I don't think that is going to do what you want. The problem is what >> happens if set and reset are on at the same time? > This would be the best case. The result will be random and we'd read an > average value of 0.5 from the flip flop. The problem is that FFs don't work that way. There are two types of FFs. SR-FFs have set and reset inputs. Set turns it on. Reset turns it off. These are level sensitive, not edge sensitive. If both set and reset are active at the same time (overlap) you have to look in the data sheet to see what happens. After the overlap, the last one active wins. Edge triggered D-FFs have data (D) and clock inputs. If D is high when clock goes high, the output will be high. If D is low when clock goes high, the output will be low. There are rules for FFs: Setup, hold, min high/low on the clock, ... Read the data sheet for the whole list. > I think you want everything to be edge triggered. The flip flop should look > only at the leading edge of each pulse. That would be handy, but I don't know of any FFs that work that way. All of the clocked FFs only have one clock. You might make it work by using the PPS as the clock with the D input hard wired to 1. That will set the FF unless the reset is active. albertson.ch...@gmail.com said: > You don't get a PPS from the OXCO. It runs at 10MHz (Or whatever you like) > so it resets the flip flop every 100 nanoseconds. > The way this works is the PPS from the GPS sets the FF to "1" once per > second and then some time later the OXCO resets it back to zero. If we > sample the FF at some fixed time after the PPS and that fixed time is less > then the OXCO period then the FF will be either 1 or 0. THe computer tries > to drive the OXCO so that the sampled value is 0.5 on average. So it looks > at the last 1000 samples and tries to hit "500". How are you going to implement that fixed time delay and sampling? I don't see a simple way to do it. What is the correct delay? How about 0? In general, when people start adding things like "fixed delays", I start thinking "kludge - there must be a better way". There is another problem with using the OCXO output (100 ns) directly. How do you eliminate aliasing/beats? Suppose the OCXO is running at exactly 9 MHz. If you average over 1000 samples, you'll get your 0.500 . If you look carefully, you can find a pattern. There is probably some simple math in here, but I'm not enough of a PLL wizard to be able to describe it. Capture range and things like that. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Hi Without a specific goal, there's no real way to pick a set of hardware. The Freescale board I mentioned earlier is a reasonably cheap (sub $15) ARM board. The only way to decide which / what to use is to have an objective. Without agreement on that we'll each just go on and on tossing up names of boards we happen to have noticed or liked … Be careful with PWM outputs for 1 pps generation. Most (but not all) PWM's have one or another gotcha when you go to use them for that task. Bob On Dec 9, 2012, at 5:43 PM, Dennis Ferguson wrote: > > On 9 Dec, 2012, at 02:14 , Hal Murray wrote: >> Which brings up another worm for the can. How are you going to get a PPS >> from the OCXO? That's going to be hard without some soldering. My straw >> man >> would be to use the OCXO to clock whatever uP you end up using and generate >> the PPS with a counter/timer. > > I think I'd do that too, and pick a processor with enough of the right > peripherals to avoid having to fart around with an external phase comparison > or interrupt timestamping. > > The TI Stellaris LaunchPad, mentioned earlier, is pretty cheap, the > processor can generate its internal clocks directly from a 10 MHz > reference input, and it has a set of 32 bit timer/counters that can either > capture a timestamp for an input edge event or generate a timed outgoing > pulse, both with a resolution of 12.5 ns. The capture could be used to > time the GPS PPS (in hardware, no external comparator, no interrupt > timestamps) while I think the PWM generation mode could be used to generate > a PPS output synchronous with the 10 MHz oscillator. The only thing that > is missing for a GPSDO is an internal DAC (it has a bunch of ADCs) so the > 10 MHz oscillator would need a digital frequency adjustment for the > processor to be sufficient for the job without any external peripherals. > The processor core is a fully functional ARM, including floating point, > which might make it easier to, say, do a Kalman filter implementation > that wasn't write-only. > > The thing is, I still don't find this all that compelling. Personally > I think it might be better to maybe aim higher on the software value > chain, find a processor board with the same on-chip processor peripherals > as above along with an on-chip Ethernet MAC and enough external peripherals > to run a real operating system and use that to build a combination GPSDO > and very accurate NTP/PTP server. You generally can't just buy one of > those on eBay (at least they are much rarer than a GPSDO alone), and it > is a lot easier to do something which is attractive both in price and in > quality compared to what you can buy. > > Dennis Ferguson > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
On 9 Dec, 2012, at 02:14 , Hal Murray wrote: > Which brings up another worm for the can. How are you going to get a PPS > from the OCXO? That's going to be hard without some soldering. My straw man > would be to use the OCXO to clock whatever uP you end up using and generate > the PPS with a counter/timer. I think I'd do that too, and pick a processor with enough of the right peripherals to avoid having to fart around with an external phase comparison or interrupt timestamping. The TI Stellaris LaunchPad, mentioned earlier, is pretty cheap, the processor can generate its internal clocks directly from a 10 MHz reference input, and it has a set of 32 bit timer/counters that can either capture a timestamp for an input edge event or generate a timed outgoing pulse, both with a resolution of 12.5 ns. The capture could be used to time the GPS PPS (in hardware, no external comparator, no interrupt timestamps) while I think the PWM generation mode could be used to generate a PPS output synchronous with the 10 MHz oscillator. The only thing that is missing for a GPSDO is an internal DAC (it has a bunch of ADCs) so the 10 MHz oscillator would need a digital frequency adjustment for the processor to be sufficient for the job without any external peripherals. The processor core is a fully functional ARM, including floating point, which might make it easier to, say, do a Kalman filter implementation that wasn't write-only. The thing is, I still don't find this all that compelling. Personally I think it might be better to maybe aim higher on the software value chain, find a processor board with the same on-chip processor peripherals as above along with an on-chip Ethernet MAC and enough external peripherals to run a real operating system and use that to build a combination GPSDO and very accurate NTP/PTP server. You generally can't just buy one of those on eBay (at least they are much rarer than a GPSDO alone), and it is a lot easier to do something which is attractive both in price and in quality compared to what you can buy. Dennis Ferguson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Hi There are other devices where a simultaneous set and reset will toggle the device. Since the "useful" operating point is simultaneous inputs, what you are building is a metastability tester. Bob On Dec 9, 2012, at 5:00 PM, Hal Murray wrote: > > li...@rtty.us said: >> The flip flop would have a metastable region. It would be quite narrow, but >> it would be there. As soon as you try to take the square wave into the >> processor, you are right back to the same problems we've discussed before. >> The flip flop, run this way does not improve that part of the situation. > > That's not the issue I was trying to bring up. > > The problem is that set and reset on most FFs are asynchronous. You have to > look at the fine print in the data sheet to see what happens if they overlap. > Consider the 74x74 that I looked at. It has true and compliment output > pins. If set and reset are both active, both outputs go high. So if the > reset signal comes first, you might expect the FF to get turned off, but with > that chip, the FF will be high. > > (A few FFs have synchronous set and reset, but since there was no mention of > a clock, I assume we are talking about asynchronous inputs.) > > > > -- > These are my opinions. I hate spam. > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
li...@rtty.us said: > The flip flop would have a metastable region. It would be quite narrow, but > it would be there. As soon as you try to take the square wave into the > processor, you are right back to the same problems we've discussed before. > The flip flop, run this way does not improve that part of the situation. That's not the issue I was trying to bring up. The problem is that set and reset on most FFs are asynchronous. You have to look at the fine print in the data sheet to see what happens if they overlap. Consider the 74x74 that I looked at. It has true and compliment output pins. If set and reset are both active, both outputs go high. So if the reset signal comes first, you might expect the FF to get turned off, but with that chip, the FF will be high. (A few FFs have synchronous set and reset, but since there was no mention of a clock, I assume we are talking about asynchronous inputs.) -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Hi In order to get a useful average, you need to have the pps arrive just a bit ahead and a bit behind the 10 MHz out of the OCXO. If the GPS PPS moves more than 100 ns between samples you get data from different cycles on the OCXO. That does not give you useful information to average. If the pps out of the GPS and the OCXO are both very accurate, you only get a one or a zero out. Again you can't average the result very well. Assuming everything is arranged "just right", you need to average a *lot* of samples to get the job done. The gain of this phase detector is highly dependent on the jitter of both the GPS and the OCXO. Since gain is critical to the setting of all the loop coefficients, that can be an issue. It also means that precise measurement of both these jitter terms is something that must be done before you are likely to come up with loop that will run without oscillation. Bob On Dec 9, 2012, at 12:03 PM, Chris Albertson wrote: > On Sat, Dec 8, 2012 at 11:14 PM, Hal Murray wrote: > >> >> albertson.ch...@gmail.com said: >>> What if I use a flip flop. The PPS from the GPS connects to the "set" >> input >>> of the FF and also to the Arduino interrupt. The output of the OCXO >> goes >>> to the reset pin of the same FF. >> >> I don't think that is going to do what you want. The problem is what >> happens >> if set and reset are on at the same time? >> > > This would be the best case. The result will be random and we'd read an > average value of 0.5 from the flip flop. > >> >> If I was doing that, I'm make the PPS from the OCXO 50% duty cycle and use >> the PPS from the GPS as a clock with the PPS from the OCXO as the data >> input. >> > > I think you want everything to be edge triggered. The flip flop should > look only at the leading edge of each pulse. > >> >> >> Which brings up another worm for the can. How are you going to get a PPS >> from the OCXO? > > > You don't get a PPS from the OXCO. It runs at 10MHz (Or whatever you like) > so it resets the flip flop every 100 nanoseconds. > > The way this works is the PPS from the GPS sets the FF to "1" once per > second and then some time later the OXCO resets it back to zero. If we > sample the FF at some fixed time after the PPS and that fixed time is less > then the OXCO period then the FF will be either 1 or 0. THe computer > tries to drive the OXCO so that the sampled value is 0.5 on average. So > it looks at the last 1000 samples and tries to hit "500". > > Basically what we have is a one bit counter but if we average enough > samples we get pretty good resolution. > > > >> That's going to be hard without some soldering. My straw man >> would be to use the OCXO to clock whatever uP you end up using and generate >> the PPS with a counter/timer. >> >> An alternative would be 7 TTL chips or a CPLD/FLGA. >> > > If you used the CPLD then you have to agree to supply programmed chips for > life and to make any change any experimenter asks for with fast turn > around. > >> >> >> -- >> These are my opinions. I hate spam. >> >> >> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > -- > > Chris Albertson > Redondo Beach, California > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
On Sat, Dec 8, 2012 at 11:14 PM, Hal Murray wrote: > > albertson.ch...@gmail.com said: > > What if I use a flip flop. The PPS from the GPS connects to the "set" > input > > of the FF and also to the Arduino interrupt. The output of the OCXO > goes > > to the reset pin of the same FF. > > I don't think that is going to do what you want. The problem is what > happens > if set and reset are on at the same time? > This would be the best case. The result will be random and we'd read an average value of 0.5 from the flip flop. > > If I was doing that, I'm make the PPS from the OCXO 50% duty cycle and use > the PPS from the GPS as a clock with the PPS from the OCXO as the data > input. > I think you want everything to be edge triggered. The flip flop should look only at the leading edge of each pulse. > > > Which brings up another worm for the can. How are you going to get a PPS > from the OCXO? You don't get a PPS from the OXCO. It runs at 10MHz (Or whatever you like) so it resets the flip flop every 100 nanoseconds. The way this works is the PPS from the GPS sets the FF to "1" once per second and then some time later the OXCO resets it back to zero. If we sample the FF at some fixed time after the PPS and that fixed time is less then the OXCO period then the FF will be either 1 or 0. THe computer tries to drive the OXCO so that the sampled value is 0.5 on average. So it looks at the last 1000 samples and tries to hit "500". Basically what we have is a one bit counter but if we average enough samples we get pretty good resolution. > That's going to be hard without some soldering. My straw man > would be to use the OCXO to clock whatever uP you end up using and generate > the PPS with a counter/timer. > > An alternative would be 7 TTL chips or a CPLD/FLGA. > If you used the CPLD then you have to agree to supply programmed chips for life and to make any change any experimenter asks for with fast turn around. > > > -- > These are my opinions. I hate spam. > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Hi The flip flop would have a metastable region. It would be quite narrow, but it would be there. As soon as you try to take the square wave into the processor, you are right back to the same problems we've discussed before. The flip flop, run this way does not improve that part of the situation. Bob On Dec 9, 2012, at 2:14 AM, Hal Murray wrote: > > albertson.ch...@gmail.com said: >> What if I use a flip flop. The PPS from the GPS connects to the "set" input >> of the FF and also to the Arduino interrupt. The output of the OCXO goes >> to the reset pin of the same FF. > > I don't think that is going to do what you want. The problem is what happens > if set and reset are on at the same time? > > If I was doing that, I'm make the PPS from the OCXO 50% duty cycle and use > the PPS from the GPS as a clock with the PPS from the OCXO as the data input. > > > Which brings up another worm for the can. How are you going to get a PPS > from the OCXO? That's going to be hard without some soldering. My straw man > would be to use the OCXO to clock whatever uP you end up using and generate > the PPS with a counter/timer. > > An alternative would be 7 TTL chips or a CPLD/FLGA. > > > -- > These are my opinions. I hate spam. > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
albertson.ch...@gmail.com said: > What if I use a flip flop. The PPS from the GPS connects to the "set" input > of the FF and also to the Arduino interrupt. The output of the OCXO goes > to the reset pin of the same FF. I don't think that is going to do what you want. The problem is what happens if set and reset are on at the same time? If I was doing that, I'm make the PPS from the OCXO 50% duty cycle and use the PPS from the GPS as a clock with the PPS from the OCXO as the data input. Which brings up another worm for the can. How are you going to get a PPS from the OCXO? That's going to be hard without some soldering. My straw man would be to use the OCXO to clock whatever uP you end up using and generate the PPS with a counter/timer. An alternative would be 7 TTL chips or a CPLD/FLGA. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Bob, Charles, Chris, If the goal is a GPS locked frequency counter then there is no need for disciplining the LO at all. Just let the XO or OCXO or Rb free-run. Use a two channel counter: one capture input to measure the frequency of the DUT and another capture input to leisurely and independently monitor the 1PPS. Over time the counter will know the frequency error (and drift) rate of the LO relative to GPS, which it then applies as a *math* correction to all DUT frequency readings before the user sees them. I do this all the time -- an XO-based picPET measuring a GPS 1PPS is really measuring the XO using GPS, not the other way around. It takes one line of code to apply a *(1+e) correction to a reading. The averaging interval over which e is calculated replaces the GPSDO time constant. Effectively you are disciplining the readings rather than the oscillator. No DAC used. This also allows you to use oscillators that lack EFC. The LO doesn't need to be a nice number like 10 MHz either. Saving e in EEPROM is effectively holdover mode. This GPSDFC is simpler than a GPSDO-frequency counter but delivers the same accuracy. Note any stable 1PPS source will do; doesn't have to be GPS. The quality of the LO determines the short gate time stability. The accuracy of the 1PPS determines the long gate time accuracy. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Hi Here's the easy way: Feed the GPS and the PPS from the OCXO into NTP. Let it discipline to the GPS and simply monitor the OCXO. That will give you all the time data you would ever need. Once a month / week run a script to steer the OCXO by the error divided by X. Play with X and you can optimize the process. Bob On Dec 8, 2012, at 8:59 PM, Bob Camp wrote: > Hi > > Have an alarm go off on your PC and do the correction once a month. > > Bob > > On Dec 8, 2012, at 8:56 PM, Chris Albertson wrote: > >> So the goal then is automate the process, not to make it better. I figure >> once you have an easy-to-modify and easy-to-replicate design up and running >> then with many people able to experiment the performance will improve. >> >> You can almost not count the cost of the Arduino. This is a self contained >> part that can be used in many projects. Same with a 12VDC power supply. >> Lots of people like to play with these and have them already. >> >> So, as for performance, let's just say for not that it only has to >> work as well as one could do by hand and eye and a 'scope. Let's say 10E-8 >> >> >> What if I use a flip flop. The PPS from the GPS connects to the "set" >> input of the FF and also to the Arduino interrupt. The output of the OCXO >> goes to the reset pin of the same FF. >> >> The interrupt handler reads the value of the FF. It will be either 1 or 0 >> depending if the phase of the OCXO leads or lags the phase of the PPS. The >> software will try to keep the FF average value at exactly 0.500 >> >> >> >> >> On Sat, Dec 8, 2012 at 4:25 PM, Bob Camp wrote: >> >>> Hi >>> >>> A standard that is good to "8 digits" can be done manually. That's far >>> cheaper than your goal and the software is totally open source. It can be >>> done with off the shelf parts and no wiring at all. >>> >>> Problem solved? >>> >>> I suspect not…. >>> >>> Bob >>> >>> On Dec 8, 2012, at 1:59 PM, Chris Albertson >>> wrote: >>> On Sat, Dec 8, 2012 at 9:30 AM, wrote: > Hello all - > > "People talk about good deals on Thunderbolts but I have > yet to see one. It seems peak Thunderbolt passed before I was > seriously looking." > > > *The box you put it in - suspending it above the bench on inspirational > thought probably > will not work. A nice box is easily $ 50.00 so who cares about adding > another flip flop or > counter at 25 cents each. The goal, well my goal is to build a GPSDO to this set of requirements 1) well under 1/2 the cost of the t-bolt. 2) can be made with common parts and skills most people have 3) is completely modifiable (open source software) So #1 above means you use a low cost box, perhaps the case and old CDROM was once housed in or maybe you gut and old PC chassis #2 pretty much means you have to keep theparts cound way down. Yes a >>> chip might cost only $1 but as soon as you get more then about three of those >>> 25 cent cips you need a PCB. PCB making is not a common everyday skill so >>> #2 means a way-low parts count #3 means the uP is gong to have to come with a very easy to use and free open source toolchain. Adruino is like that, there are others, but a >>> bare uP chip is not going to work You are right that one way to engineer a product is to first set performance numbers. But another more common way is to first identify a target customer and then set a target price. In this case the target customer is a hobbyist with only basic skills who wants a low cost easy >>> to build GPSDO that has can understand and modify himself. Next with those very hard to meet requirements (low cost, low parts >>> count, simple to build) we can ask if the exected perfomance is "good enough" What is good enough. I'd say if you could use the GPSDO a a local frequency standard for a counter that has 8 digits you are doing "well enough". If you can get to 10 digital it is pretty good -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. >>> >>> >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> >> >> -- >> >> Chris Albertson >> Redondo Beach, California >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > ___
Re: [time-nuts] GPS DO Alternatives
Hi Have an alarm go off on your PC and do the correction once a month. Bob On Dec 8, 2012, at 8:56 PM, Chris Albertson wrote: > So the goal then is automate the process, not to make it better. I figure > once you have an easy-to-modify and easy-to-replicate design up and running > then with many people able to experiment the performance will improve. > > You can almost not count the cost of the Arduino. This is a self contained > part that can be used in many projects. Same with a 12VDC power supply. > Lots of people like to play with these and have them already. > > So, as for performance, let's just say for not that it only has to > work as well as one could do by hand and eye and a 'scope. Let's say 10E-8 > > > What if I use a flip flop. The PPS from the GPS connects to the "set" > input of the FF and also to the Arduino interrupt. The output of the OCXO > goes to the reset pin of the same FF. > > The interrupt handler reads the value of the FF. It will be either 1 or 0 > depending if the phase of the OCXO leads or lags the phase of the PPS. The > software will try to keep the FF average value at exactly 0.500 > > > > > On Sat, Dec 8, 2012 at 4:25 PM, Bob Camp wrote: > >> Hi >> >> A standard that is good to "8 digits" can be done manually. That's far >> cheaper than your goal and the software is totally open source. It can be >> done with off the shelf parts and no wiring at all. >> >> Problem solved? >> >> I suspect not…. >> >> Bob >> >> On Dec 8, 2012, at 1:59 PM, Chris Albertson >> wrote: >> >>> On Sat, Dec 8, 2012 at 9:30 AM, wrote: >>> Hello all - "People talk about good deals on Thunderbolts but I have yet to see one. It seems peak Thunderbolt passed before I was seriously looking." *The box you put it in - suspending it above the bench on inspirational thought probably will not work. A nice box is easily $ 50.00 so who cares about adding another flip flop or counter at 25 cents each. >>> >>> >>> >>> The goal, well my goal is to build a GPSDO to this set of requirements >>> >>> 1) well under 1/2 the cost of the t-bolt. >>> 2) can be made with common parts and skills most people have >>> 3) is completely modifiable (open source software) >>> >>> So #1 above means you use a low cost box, perhaps the case and old CDROM >>> was once housed in or maybe you gut and old PC chassis >>> >>> #2 pretty much means you have to keep theparts cound way down. Yes a >> chip >>> might cost only $1 but as soon as you get more then about three of those >> 25 >>> cent cips you need a PCB. PCB making is not a common everyday skill so >> #2 >>> means a way-low parts count >>> >>> #3 means the uP is gong to have to come with a very easy to use and free >>> open source toolchain. Adruino is like that, there are others, but a >> bare >>> uP chip is not going to work >>> >>> >>> You are right that one way to engineer a product is to first set >>> performance numbers. But another more common way is to first identify a >>> target customer and then set a target price. In this case the target >>> customer is a hobbyist with only basic skills who wants a low cost easy >> to >>> build GPSDO that has can understand and modify himself. >>> >>> Next with those very hard to meet requirements (low cost, low parts >> count, >>> simple to build) we can ask if the exected perfomance is "good enough" >>> What is good enough. I'd say if you could use the GPSDO a a local >>> frequency standard for a counter that has 8 digits you are doing "well >>> enough". If you can get to 10 digital it is pretty good >>> >>> -- >>> >>> Chris Albertson >>> Redondo Beach, California >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > -- > > Chris Albertson > Redondo Beach, California > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
So the goal then is automate the process, not to make it better. I figure once you have an easy-to-modify and easy-to-replicate design up and running then with many people able to experiment the performance will improve. You can almost not count the cost of the Arduino. This is a self contained part that can be used in many projects. Same with a 12VDC power supply. Lots of people like to play with these and have them already. So, as for performance, let's just say for not that it only has to work as well as one could do by hand and eye and a 'scope. Let's say 10E-8 What if I use a flip flop. The PPS from the GPS connects to the "set" input of the FF and also to the Arduino interrupt. The output of the OCXO goes to the reset pin of the same FF. The interrupt handler reads the value of the FF. It will be either 1 or 0 depending if the phase of the OCXO leads or lags the phase of the PPS. The software will try to keep the FF average value at exactly 0.500 On Sat, Dec 8, 2012 at 4:25 PM, Bob Camp wrote: > Hi > > A standard that is good to "8 digits" can be done manually. That's far > cheaper than your goal and the software is totally open source. It can be > done with off the shelf parts and no wiring at all. > > Problem solved? > > I suspect not…. > > Bob > > On Dec 8, 2012, at 1:59 PM, Chris Albertson > wrote: > > > On Sat, Dec 8, 2012 at 9:30 AM, wrote: > > > >> Hello all - > >> > >> "People talk about good deals on Thunderbolts but I have > >> yet to see one. It seems peak Thunderbolt passed before I was > >> seriously looking." > >> > >> > >> *The box you put it in - suspending it above the bench on inspirational > >> thought probably > >> will not work. A nice box is easily $ 50.00 so who cares about adding > >> another flip flop or > >> counter at 25 cents each. > > > > > > > > The goal, well my goal is to build a GPSDO to this set of requirements > > > > 1) well under 1/2 the cost of the t-bolt. > > 2) can be made with common parts and skills most people have > > 3) is completely modifiable (open source software) > > > > So #1 above means you use a low cost box, perhaps the case and old CDROM > > was once housed in or maybe you gut and old PC chassis > > > > #2 pretty much means you have to keep theparts cound way down. Yes a > chip > > might cost only $1 but as soon as you get more then about three of those > 25 > > cent cips you need a PCB. PCB making is not a common everyday skill so > #2 > > means a way-low parts count > > > > #3 means the uP is gong to have to come with a very easy to use and free > > open source toolchain. Adruino is like that, there are others, but a > bare > > uP chip is not going to work > > > > > > You are right that one way to engineer a product is to first set > > performance numbers. But another more common way is to first identify a > > target customer and then set a target price. In this case the target > > customer is a hobbyist with only basic skills who wants a low cost easy > to > > build GPSDO that has can understand and modify himself. > > > > Next with those very hard to meet requirements (low cost, low parts > count, > > simple to build) we can ask if the exected perfomance is "good enough" > > What is good enough. I'd say if you could use the GPSDO a a local > > frequency standard for a counter that has 8 digits you are doing "well > > enough". If you can get to 10 digital it is pretty good > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > ___ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Hi A little math: You can get an OCXO that will do 1x10^-10 per day and has a sub 5x10^-10 temp performance. It's likely that the temperature impact will be minimal in a normal environment. If you are after 1x10^-8, you need to correct roughly every 100 days. That's not anything you need a cpu to handle. Even if you are after 1x10^-9, the aging is likely predictable. A bump every 10 days and a measurement once a month likely does the trick. Still not much of a need for a CPU. For a much easier / cheaper / less work solution - grab a cheap rubidium. Manually set it to ~ 1x10^-11. It will hold your 9 digits for at least a year. With some luck I'll hold 10 digits. Bob On Dec 8, 2012, at 1:59 PM, Chris Albertson wrote: > On Sat, Dec 8, 2012 at 9:30 AM, wrote: > >> Hello all - >> >> "People talk about good deals on Thunderbolts but I have >> yet to see one. It seems peak Thunderbolt passed before I was >> seriously looking." >> >> >> *The box you put it in - suspending it above the bench on inspirational >> thought probably >> will not work. A nice box is easily $ 50.00 so who cares about adding >> another flip flop or >> counter at 25 cents each. > > > > The goal, well my goal is to build a GPSDO to this set of requirements > > 1) well under 1/2 the cost of the t-bolt. > 2) can be made with common parts and skills most people have > 3) is completely modifiable (open source software) > > So #1 above means you use a low cost box, perhaps the case and old CDROM > was once housed in or maybe you gut and old PC chassis > > #2 pretty much means you have to keep theparts cound way down. Yes a chip > might cost only $1 but as soon as you get more then about three of those 25 > cent cips you need a PCB. PCB making is not a common everyday skill so #2 > means a way-low parts count > > #3 means the uP is gong to have to come with a very easy to use and free > open source toolchain. Adruino is like that, there are others, but a bare > uP chip is not going to work > > > You are right that one way to engineer a product is to first set > performance numbers. But another more common way is to first identify a > target customer and then set a target price. In this case the target > customer is a hobbyist with only basic skills who wants a low cost easy to > build GPSDO that has can understand and modify himself. > > Next with those very hard to meet requirements (low cost, low parts count, > simple to build) we can ask if the exected perfomance is "good enough" > What is good enough. I'd say if you could use the GPSDO a a local > frequency standard for a counter that has 8 digits you are doing "well > enough". If you can get to 10 digital it is pretty good > > -- > > Chris Albertson > Redondo Beach, California > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Hi A standard that is good to "8 digits" can be done manually. That's far cheaper than your goal and the software is totally open source. It can be done with off the shelf parts and no wiring at all. Problem solved? I suspect not…. Bob On Dec 8, 2012, at 1:59 PM, Chris Albertson wrote: > On Sat, Dec 8, 2012 at 9:30 AM, wrote: > >> Hello all - >> >> "People talk about good deals on Thunderbolts but I have >> yet to see one. It seems peak Thunderbolt passed before I was >> seriously looking." >> >> >> *The box you put it in - suspending it above the bench on inspirational >> thought probably >> will not work. A nice box is easily $ 50.00 so who cares about adding >> another flip flop or >> counter at 25 cents each. > > > > The goal, well my goal is to build a GPSDO to this set of requirements > > 1) well under 1/2 the cost of the t-bolt. > 2) can be made with common parts and skills most people have > 3) is completely modifiable (open source software) > > So #1 above means you use a low cost box, perhaps the case and old CDROM > was once housed in or maybe you gut and old PC chassis > > #2 pretty much means you have to keep theparts cound way down. Yes a chip > might cost only $1 but as soon as you get more then about three of those 25 > cent cips you need a PCB. PCB making is not a common everyday skill so #2 > means a way-low parts count > > #3 means the uP is gong to have to come with a very easy to use and free > open source toolchain. Adruino is like that, there are others, but a bare > uP chip is not going to work > > > You are right that one way to engineer a product is to first set > performance numbers. But another more common way is to first identify a > target customer and then set a target price. In this case the target > customer is a hobbyist with only basic skills who wants a low cost easy to > build GPSDO that has can understand and modify himself. > > Next with those very hard to meet requirements (low cost, low parts count, > simple to build) we can ask if the exected perfomance is "good enough" > What is good enough. I'd say if you could use the GPSDO a a local > frequency standard for a counter that has 8 digits you are doing "well > enough". If you can get to 10 digital it is pretty good > > -- > > Chris Albertson > Redondo Beach, California > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
I've only been following this thread distantly, however, I have been playing with arduinos quite a bit of late. If you wanted to incorporate one as the processor of choice in a new design, the cost is quite low, under $4.00us for the processor in quantity one. I've used one in a new design in the last week and it really simplified life. As to the capabilities, remember that pretty much any AVR chip can run the arduino code. The atmega128 has more oomph for about the same price for example. Additionally, if you don't like the language for the arduino, C takes about 5 minutes to get running. Bob On Dec 8, 2012, at 17:52, Jim Lux wrote: > On 12/8/12 9:30 AM, johncr...@aol.com wrote: >> >> >> Instead the discussion has centered on what microprocessor (of a hundred >> that would work) >> and how to eliminate "glue" logic and and a few analog parts to save >> money. This is silly - silicon is >> CHEAP. > > Silicon is cheap, but for one-off fabrication by a hobbyist that isn't always > the case. As was mentioned in a couple of the mails in the long discussion, > for a single person to build something like this requires a combination of > skills and materials. Someone may be fine at software, but doesn't want to > fabricate circuitry, or vice versa. > > So, there was discussion of what could you do that would literally be "plug > and play" with minimal hardware design and assembly required (so the playing > would be with software). > > > This isn't an unusual scenario.. The AMSAT folks have run into it vis a vis > ground stations. So have others (APRS). A colleague of mine (N5BF) comments > that what you really need is something where someone can "impulse buy" enough > to do something useful fairly quickly. The "kit idea": buying $100 worth of > parts and then having to spend 6 weeks assembling and testing means that lots > of people will have $100 parts bags sitting on a shelf, unused. You'd be > better off selling a $200 assembled and tested widget. Yes, you won't sell > quite as many, but a LOT more of them will be actually used than those bags > o'parts. > > > A particularly attractive model is where you have a hardware component that > is delivered pretty much ready to go, with basic software, and the "fooling > around" is with changes in the software or parameters. For the GPSDO world, > this might be experimenting with different filters and holdover strategies, > or maybe tuning it to work with your particular OCXO. > > This is why the Arduino is so popular. No or minimal soldering required, a > wealth of simple software that almost does what you need it to, be it > monitoring the temperature of your beer fermentation, turning on and off > sprinklers or whatever. > > Anything where the software is quite complex, that will inhibit > experimentation, unless there's a lot of documentation of the theory of > operation and software design, and the software has to be written to > facilitate modification. For the Arduino, the limited amount of storage > sort of self limits the complexity of applications. Once you move into the > PC world it gets a lot harder. And realistically, a lot of hobby written > software doesn't have a good architecture or underlying design. It sort of > just growed in place with successive modifications to add features, etc. And > it works, but it's not very easy to figure out how to modify it. > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
On 12/8/12 9:30 AM, johncr...@aol.com wrote: Instead the discussion has centered on what microprocessor (of a hundred that would work) and how to eliminate "glue" logic and and a few analog parts to save money. This is silly - silicon is CHEAP. Silicon is cheap, but for one-off fabrication by a hobbyist that isn't always the case. As was mentioned in a couple of the mails in the long discussion, for a single person to build something like this requires a combination of skills and materials. Someone may be fine at software, but doesn't want to fabricate circuitry, or vice versa. So, there was discussion of what could you do that would literally be "plug and play" with minimal hardware design and assembly required (so the playing would be with software). This isn't an unusual scenario.. The AMSAT folks have run into it vis a vis ground stations. So have others (APRS). A colleague of mine (N5BF) comments that what you really need is something where someone can "impulse buy" enough to do something useful fairly quickly. The "kit idea": buying $100 worth of parts and then having to spend 6 weeks assembling and testing means that lots of people will have $100 parts bags sitting on a shelf, unused. You'd be better off selling a $200 assembled and tested widget. Yes, you won't sell quite as many, but a LOT more of them will be actually used than those bags o'parts. A particularly attractive model is where you have a hardware component that is delivered pretty much ready to go, with basic software, and the "fooling around" is with changes in the software or parameters. For the GPSDO world, this might be experimenting with different filters and holdover strategies, or maybe tuning it to work with your particular OCXO. This is why the Arduino is so popular. No or minimal soldering required, a wealth of simple software that almost does what you need it to, be it monitoring the temperature of your beer fermentation, turning on and off sprinklers or whatever. Anything where the software is quite complex, that will inhibit experimentation, unless there's a lot of documentation of the theory of operation and software design, and the software has to be written to facilitate modification. For the Arduino, the limited amount of storage sort of self limits the complexity of applications. Once you move into the PC world it gets a lot harder. And realistically, a lot of hobby written software doesn't have a good architecture or underlying design. It sort of just growed in place with successive modifications to add features, etc. And it works, but it's not very easy to figure out how to modify it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Chris wrote: The goal, well my goal is to build a GPSDO to this set of requirements 1) well under 1/2 the cost of the t-bolt. 2) can be made with common parts and skills most people have 3) is completely modifiable (open source software) * * * if you could use the GPSDO a a local frequency standard for a counter that has 8 digits you are doing "well enough". If you can get to 10 digital it is pretty good OK, if we assume that a Thunderbolt is < $200 these days, the GPSDO module (no PS, no antenna) needs to be "well under" $100. So, $75-80? And to be clearly good enough for an 8-digit counter with one-digit overrange using gate times of 1 and 10 seconds, it should have an ADEV ~ 1e-10 at tau = 1 and 10 seconds. Go down one power of ten for each digit over 8, and up one if the counter does not have overrange. The performance at tau = 1 and 10 seconds will be largely dependent on the quartz oscillator used, assuming that its performance over the next two or three decades allows one to set the time constant of the discipline loop out in the 500 second range. 1e-10 is a bit more than one order of magnitude worse than an average Thunderbolt. [1e-12 (what you would need for a 10-digit counter with one digit overrange) is somewhat better than you can expect from an average Thunderbolt. 1e-11 (what you would need for a 10-digit counter with no overrange, or a 9-digit counter with one digit overrange) is just about what an average Thunderbolt delivers.] The holdover performance of the DIY box would likely not be as good as the Thunderbolt, because any sub-$100 implementation that can be made with common parts and the skills most people have is unlikely to include Kalman filtering or other predictive steering during holdover (but as I said in a previous message, holdover performance may not be required by many amateur time nuts, who can simply restrict their use of the standard to periods when it is performing nominally). As we have discussed many times here, the control loop is much easier to design if it is comparing the 10 MHz output to a frequency much higher than 1 Hz. This is why the original Miller DIY GPSDO (http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm) (http://www.jrmiller.demon.co.uk/projects/ministd/manual.pdf) is able to achieve such good results (comparable to an average Thunderbolt) with a very simple design -- it uses Jupiter GPS engines with a disciplined 10 kHz output. I believe the PC card may still be available, for those who can find a Jupiter to use it with. (Note that Mr. Miller also supplies a ready-made version of the GPSDO with Axtal OXCO, but that one costs well more than a Thunderbolt.) The design goals stated above are ambitious, and I suspect it will be a challenge to come in on budget even with the relaxed stability requirement compared to a Thunderbolt. But I do hope you give it a go, and will be most interested to see what you come up with. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
On Sat, Dec 8, 2012 at 9:30 AM, wrote: > Hello all - > > "People talk about good deals on Thunderbolts but I have > yet to see one. It seems peak Thunderbolt passed before I was > seriously looking." > > > *The box you put it in - suspending it above the bench on inspirational > thought probably > will not work. A nice box is easily $ 50.00 so who cares about adding > another flip flop or > counter at 25 cents each. The goal, well my goal is to build a GPSDO to this set of requirements 1) well under 1/2 the cost of the t-bolt. 2) can be made with common parts and skills most people have 3) is completely modifiable (open source software) So #1 above means you use a low cost box, perhaps the case and old CDROM was once housed in or maybe you gut and old PC chassis #2 pretty much means you have to keep theparts cound way down. Yes a chip might cost only $1 but as soon as you get more then about three of those 25 cent cips you need a PCB. PCB making is not a common everyday skill so #2 means a way-low parts count #3 means the uP is gong to have to come with a very easy to use and free open source toolchain. Adruino is like that, there are others, but a bare uP chip is not going to work You are right that one way to engineer a product is to first set performance numbers. But another more common way is to first identify a target customer and then set a target price. In this case the target customer is a hobbyist with only basic skills who wants a low cost easy to build GPSDO that has can understand and modify himself. Next with those very hard to meet requirements (low cost, low parts count, simple to build) we can ask if the exected perfomance is "good enough" What is good enough. I'd say if you could use the GPSDO a a local frequency standard for a counter that has 8 digits you are doing "well enough". If you can get to 10 digital it is pretty good -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS DO Alternatives
Hello all - "People talk about good deals on Thunderbolts but I have yet to see one. It seems peak Thunderbolt passed before I was seriously looking." I would suggest some more serious looking. This guy "TRIMBLE GPS RECEIVER 10MHZ CLOCK THUNDERBOLT" currently has more than 10 T-bolts for sale on eBay as of this morning for $ 175. Last summer I bought 3 of his units and all were in great condition and worked just fine. the one pictured and all of the ones I obtained had a nice MiniCircuits 2 way splitter that came with it. The splitter is about $ 50 new and usable at 10 MHz and over a wide bandwidth. In fact during the several days of lamenting the lack of T bolts there were several vendors offering them for various prices from good to not so good. As to building a GPS DO some of the recent comments from persons dedicated to precision time and frequency - apparently willing to go to extreme measure to achieve it seem curious to say the least. Here performance seemed to be unspecified and of less importance than what uP to use. As usual there was the temptation to jump to implementations without the steps essential to any good design to wit: 1. A agreed to requirements document 2. A peer reviewed specification 3. A conceptual design and conceptual packaging concepts (What should the box cost?) 4. A conceptual design review 5. A preliminary circuit design, SW design, and final package concept. 6. Implementation and test of the preliminary circuit and SW design. 7. Incorporation of the test results and final design release. Instead the discussion has centered on what microprocessor (of a hundred that would work) and how to eliminate "glue" logic and and a few analog parts to save money. This is silly - silicon is CHEAP. Major cost items not considered include - somewhat in order of decreasing cost : *The box you put it in - suspending it above the bench on inspirational thought probably will not work. A nice box is easily $ 50.00 so who cares about adding another flip flop or counter at 25 cents each. *The printed wiring board. Most costly per unit up to about 4 pieces * A power supply - you will need a good low noise one. * OCXO So when you look at the total system - any GPS DO when fully developed and packaged into a unit with long term reliability and performance acceptable to this group is a non-trivial project. It is, however a challenging and rewarding project - particularly if well done. -73 john k6iql -Original Message- From: time-nuts-request To: time-nuts Sent: Sat, Dec 8, 2012 2:56 am Subject: time-nuts Digest, Vol 101, Issue 63 Send time-nuts mailing list submissions to time-nuts@febo.com To subscribe or unsubscribe via the World Wide Web, visit https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts or, via email, send a message with subject or body 'help' to time-nuts-requ...@febo.com You can reach the person managing the list at time-nuts-ow...@febo.com When replying, please edit your Subject line so it is more specific than "Re: Contents of time-nuts digest..." Today's Topics: 1. Re: GPSDO Alternatives - Bert's boards (WB6BNQ) 2. Re: PPS offset between GPS receivers (Chris Albertson) 3. Re: GPSDO Alternatives (David) 4. Re: PPS offset between GPS receivers (Bob Camp) 5. Re: Open source (Poul-Henning Kamp) 6. Re: Open source (David Kirkby) 7. Re: Termination talk (Attila Kinali) -- Message: 1 Date: Fri, 07 Dec 2012 18:06:17 -0800 From: WB6BNQ To: Discussion of precise time and frequency measurement , ewkeh...@aol.com Subject: Re: [time-nuts] GPSDO Alternatives - Bert's boards Message-ID: <50c2a099.cbfda...@cox.net> Content-Type: text/plain; charset=us-ascii Hello Bert, The boards look nice but tell me nothing of the circuitry. How about sending the schematics ?? That way I can appreciate what it is that you have. BillWB6BNQ p.s. By the way, what ever happen with that DMTD you were going to produce about three years ago ? ewkeh...@aol.com wrote: Attached is my latest ExpresPCB layout of a GPSDO. A clear understanding of the GPS limitations, a goal as to what I want to control ,focus on attainability, reproducibility KISS, cost and tests of partials on development boards and what you see if you download the ExpessPCB software is on the right the saw tooth correction, in the middle the analog board with opto isolation to prevent ground loop and on the right the actual GPSDO. This particular unit also allows you to link a 20 Hz offset FRS-C (part of my dual mixer) to my house reference. Total material cost depending how many boards one buys is below $ 40. I will include this particular board along with other designs on my next order and subsequently cut with a sheer. The board on the right could be used by itself with minor modifications to directly drive a FE 56
